Evidence that RNA 4 of alfalfa mosaic virus does not replicate autonomously.

A mutant (Tbts7) of alfalfa mosaic virus, the coat protein of which is unable to activate the viral genome (the RNA species 1, 2, and 3, which need some coat protein for infectivity) at 30 degrees , can be rescued at this temperature by adding to the inoculum wild-type RNA 3 (the genome part that contains the coat protein cistron), but not adding wild-type RNA 4 (the subgenomic messenger for the coat protein). Unless RNA 3 of Tbts 7 has a second ts mutation at a site not occurring in RNA 4, it may be concluded from the above finding that RNA 4 does not replicate autonomously.